Sheet manufacturing apparatus and sheet manufacturing method

ABSTRACT

A sheet manufacturing apparatus includes a forming unit configured to form a continuous sheet. The forming unit includes a deposition unit configured to deposit a material containing fiber, a pressurizing unit configured to pressurize a deposited web, and a heating unit configured to heat the web. The forming unit further includes a detection unit. The detection unit may be an optical sensor including a light source configured to emit light from a side of one surface of the continuous sheet (or a single sheet) and a light receiver configured to receive the light on a side of the other surface. The texture may be detected by the optical sensor over the entire surface of the continuous sheet.

BACKGROUND

1. Technical Field

The present invention relates to a sheet manufacturing apparatus and a sheet manufacturing method.

2. Related Art

There has hitherto been known a sheet manufacturing apparatus that manufactures sheets by using waste paper as a raw material. JP-A-2012-144819 describes a paper recycling apparatus that forms paper by defibrating pieces of paper into fibers by a dry-type defibrating machine. The paper recycling apparatus described in JP-A-2012-144819 manufactures sheets of a desired size by cutting a formed web (recycled paper) in a direction intersecting the transfer direction of the web by a cutting machine.

However, when such a paper recycling apparatus manufactures a sheet by using waste paper as the raw material, the sheet sometimes partly becomes black. When the dry-type defibrating machine is used, lumps of fibers are sometimes mixed in the sheet. In not only the dry-type paper recycling apparatus but also a wet-type paper recycling apparatus, a sheet is sometimes creased by pressure and heat during manufacturing. Further, since fibers are deposited on a mesh-like moving object, deposition on the sheet sometimes becomes uneven.

SUMMARY

An advantage of some aspects of the invention is to provide a sheet manufacturing apparatus that can detect the texture of a sheet.

A sheet manufacturing apparatus according to an aspect of the invention includes a forming unit that configured to form a sheet by depositing, pressurizing, and heating a material containing fiber, and a detection unit configured to detect a texture of the sheet.

In this sheet manufacturing apparatus, the texture of a sheet can be detected by the detection unit, and a defective sheet can be detected by using the detection result.

It is preferable that the detection unit should be an optical sensor configured to emit light from a side of one surface of the sheet, receive the light on a side of the other surface of the sheet, and detect the texture of an entire surface of the sheet.

In this sheet manufacturing apparatus, even when there is a defect in a part of the sheet, it can be detected by detecting the entire surface of the sheet with the optical sensor.

It is preferable that the sheet manufacturing apparatus should further include a stack unit on which the sheet is stacked when the texture of the sheet is relatively good, and a path configured to prevent the sheet from going to the stack unit when the texture of the sheet is relatively bad.

In this sheet manufacturing apparatus, since a sheet having a relatively bad texture is transferred through a path different from that for a sheet having a relatively good texture, it can be separated from the sheet having the relatively good texture.

It is preferable that the sheet manufacturing apparatus should further include an application unit configured to apply a marking on the sheet when the texture of the sheet is relatively bad.

In this sheet manufacturing apparatus, the texture can be recognized as being relatively bad by applying the marking on the sheet by the application unit.

A sheet manufacturing method according to another aspect of the invention includes forming a sheet by depositing, pressurizing, and heating a material containing fiber, and detecting a texture of the sheet.

In this sheet manufacturing method, the texture of the sheet can be detected, and a defective sheet can be detected by using the detection result.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.

FIG. 1 schematically illustrates a sheet manufacturing apparatus according to an embodiment.

FIG. 2 is a side view schematically illustrating a detection unit and a switch unit in the sheet manufacturing apparatus of the embodiment.

FIG. 3 is a plan view schematically illustrating the detection unit in the sheet manufacturing apparatus of the embodiment.

FIG. 4A is a graph showing the intensity of transmitted light in the widthwise direction of a sheet, and

FIG. 4B is a graph obtained by subjecting the graph of FIG. 4A to moving-averaging processing.

FIG. 5 is a histogram of the intensity of the transmitted light in a sheet plane.

FIG. 6 is a side view schematically illustrating a detection unit and an application unit in a first modification of the sheet manufacturing apparatus of the embodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

A preferred embodiment of the invention will be described in detail below with reference to the drawings. The embodiment which will be described hereinafter does not unduly limit the contents of the invention described in the claims. All configurations which will be described hereinafter are not essential constituent elements of the invention.

1. Sheet Manufacturing Apparatus 1.1 Configuration

First, a sheet manufacturing apparatus according to an embodiment will be described with reference to the drawings. FIG. 1 schematically illustrates a sheet manufacturing apparatus 100 according to the embodiment.

As illustrated in FIG. 1, the sheet manufacturing apparatus 100 includes a supplying unit 10, a manufacturing unit 102, and a control unit 140. The manufacturing unit 102 manufactures a sheet. The manufacturing unit 102 includes a crushing unit 12, a defibrating unit 20, a classifying unit 30, a screening unit 40, a mixing unit 50, a deposition unit 60, a web forming unit 70, a sheet forming unit 80, and a cutting unit 90.

The supplying unit 10 supplies a raw material to the crushing unit 12. For example, the supplying unit 10 is an automatic feeding unit that continuously feeds the raw material to the crushing unit 12.

The crushing unit 12 cuts the raw material supplied by the supplying unit 10 into small pieces in the air. For example, the small pieces are shaped to have a size of several centimeters square. In the example of FIG. 1, the crushing unit 12 has a crushing blade 14, and can cut the fed raw material with the crushing blade 14. As the crushing unit 12, a shredder is used as an example. The raw material cut by the crushing unit 12 is received by a hopper 1 and then transferred (conveyed) to the defibrating unit 20 through a pipe 2.

The defibrating unit 20 defibrates the raw material cut by the crushing unit 12. Here, the term “defibrate” means to untangle a raw material (defibration object) obtained by bonding a plurality of fibers into discrete fibers. The defibrating unit 20 also has the function of separating substances attached to the raw material, such as resin grains, ink, toner, and a blur-preventing agent, from the fibers.

The raw material having passed through the defibrating unit 20 is referred to as a “defibrated material.” Besides untangled defibrated material fibers, the “defibrated material” sometimes includes grains of resin (resin for bonding a plurality of fibers), coloring agents, such as ink and toner, and additive agents such as a blur-preventing agent and a paper-force increasing agent, which are separated from the fibers when the fibers are untangled. The defibrated material is untangled in a string or ribbon shape. The defibrated material may exist in a state in which it does not tangle with other untangled fibers (an independent state), or may exist in a state in which it tangles with other untangled defibrated materials into a bundle (a state in which so-called “lumps” are formed).

The defibrating unit 20 performs defibration in a dry method in the atmosphere (air). Specifically, an impeller mill is used as the defibrating unit 20. The defibrating unit 20 has the function of generate an airflow for sucking the raw material and discharging the defibrated material. By virtue of the generated airflow, the defibrating unit 20 can suck the raw material together with the airflow from an introduction port 22, defibrate the raw material, and transfer the raw material to a discharge port 24. The defibrated material having passed through the defibrating unit 20 is transferred to the classifying unit 30 through a pipe 3.

The classifying unit 30 classifies the defibrated material that has passed through the defibrating unit 20. Specifically, the classifying unit 30 separates and removes a material having a relatively small size or low density (for example, resin grains, a color agent, and an additive agent) from the defibrated material. This can increase the ratio of fibers having a relatively large size or high density to the defibrated material.

As the classifying unit 30, an airflow classifier is used. The airflow classifier generates a swirling airflow and separates the defibrated material by the difference in received centrifugal force according to the size and density of the material to be classified, and the classification point can be controlled by adjusting the speed of the airflow and the centrifugal force. Specifically, for example, a cyclone, an elbow jet, or an eddy classifier is used as the classifying unit 30. In particular, the illustrated cyclone can be suitably used as the classifying unit 30 because of its simple structure.

For example, the classifying unit 30 includes an introduction port 31, a cylindrical part 32 to which the introduction port 31 is connected, an inverted cone part 33 located under the cylindrical part 32 and continuing from the cylindrical part 32, a lower discharge port 34 provided in the center of a lower portion of the inverted cone part 33, and an upper discharge port 35 provided in the center of an upper portion of the cylindrical part 32.

In the classifying unit 30, the motion of an airflow carrying the defibrated material introduced from the introduction port 31 is changed into a circumferential motion in the cylindrical part 32. Thus, centrifugal force acts on the introduced defibrated material, and the classifying unit 30 can separate the defibrated material into fibers having a larger size and a higher density than those of resin grains and ink grains (a first classified material) and resin grains, a coloring agent, an additive agent, and so on having a smaller size and a lower density than those of the fibers (a second classified material). The first classified material is discharged from the lower discharge port 34, and is introduced into the screening unit 40 through a pipe 4. On the other hand, the second classified material is discharged from the upper discharge port 35 to a receiving unit 36 through a pipe 5.

The screening unit 40 introduces the first classified material having passed through the classifying unit 30 from an introduction port 42, and screens the first classified material according to the fiber length. For example, a sieve is used as the screening unit 40. The screening unit 40 includes a net (filter, screen), and can separate the first classified material into fibers or grains having a smaller size than the mesh size of the net (a first screened material that can pass through the net) and fibers, unfibrated pieces, and lumps having a larger size than the mesh size of the net (a second screened material that does not pass through the net). For example, the first screened material is received by a hopper 6 and is transferred to the mixing unit 50 through a pipe 7. The second screened material is returned from a discharge port 44 to the defibrating unit 20 through a pipe 8. Specifically, the screening unit 40 is a cylindrical sieve that can be rotated by a motor. For example, the net of the screening unit 40 is a metal net, an expanded metal formed by expanding a metal plate having slits, or a punching metal formed by making holes in a metal plate with a pressing machine.

The mixing unit 50 mixes the first screened material having passed through the screening unit 40 and an additive agent containing resin. The mixing unit 50 includes an additive-agent supply unit 52 for supplying an additive agent, a pipe 54 for transferring the first screened material and the additive agent, and a blower 56. In the example of FIG. 1, the additive agent is supplied from the additive-agent supply unit 52 to the pipe 54 through a hopper 9. The pipe 54 continues from the pipe 7.

In the mixing unit 50, an airflow can be generated by the blower 56, and the first screened material and the additive agent can be transferred while being mixed in the pipe 54. A mechanism for mixing the first screened material and the additive agent is not particularly limited. The mechanism may agitate the first screened material and the additive agent by a blade rotating at high speed, or may utilize the rotation of a container like a V-shaped mixer.

As the additive-agent supply unit 52, a screw feeder illustrated in FIG. 1 or a disc feeder (not illustrated) is used. The additive agent supplied from the additive-agent supply unit 52 contains resin for bonding a plurality of fibers. At the time when the resin is supplied, the plurality of fibers are not bonded. The resin melts when passing through the sheet forming unit 80, and thereby bonds the plurality of fibers.

The resin supplied from the additive-agent supply unit 52 is thermoplastic resin or heat-curable resin, and examples of the resin include AS resin, ABS resin, polypropylene, polyethylene, polyvinyl chloride, polystyrene, acrylic resin, polyester resin, polyethylene terephthalate, polyphenylene ether, polybutylene terephthalate, nylon, polyamide, polycarbonate, polyacetal, polyphenylenesulfide, and polyetheretherketone. These resins may be used alone or may be appropriately mixed. The additive agent supplied from the additive-agent supply unit 52 may be in the fiber form or powder form.

The additive agent supplied from the additive-agent supply unit 52 may contain a coloring agent for coloring the fibers, a coagulation inhibitor for inhibiting coagulation of the fibers, and a fire retardant agent for retarding firing of the fibers and the like, besides the resin for bonding the fibers. A mixture (a mixture of the first classified material and the additive agent) that has passed through the mixing unit 50 is transferred to the deposition unit 60 through the pipe 54.

In the deposition unit 60, the mixture having passed through the mixing unit 50 is introduced from an introduction port 62, and the tangled defibrated material (fibers) is untangled and dropped while being dispersed in the air. Further, in the deposition unit 60, when the resin serving as the additive agent supplied from the additive-agent supply unit 52 is in the fiber form, the resin is untangled. Thus, the deposition unit 60 allows the mixture to be uniformly deposited in the web forming unit 70.

As the deposition unit 60, a rotating cylindrical sieve is used. The deposition unit 60 includes a net, and drops fibers or grains having a size smaller than the mesh size of the net, which are contained in the mixture having passed through the mixing unit 50, (fibers or grains that can pass through the net). For example, the structure of the deposition unit 60 is the same as that of the screening unit 40.

In the deposition unit 60, the “sieve” does not always need to have the function of selecting a specific object. That is, the “sieve” used as the deposition unit 60 refers to the one having a net, and the deposition unit 60 may drop all of the mixture introduced therein.

The web forming unit 70 forms a web W by depositing the the passing-through material that has passed through the deposition unit 60. For example, the web forming unit 70 includes a mesh belt 72, stretching rollers 74, and a suction mechanism 76.

The passing-through material having passed through apertures of the deposition unit 60 (apertures of the net) is deposited on the mesh belt 72 that is moving. The mesh belt 72 is stretched by the stretching rollers 74. The mesh belt 72 hardly transmits the passing-through material, but easily transmits air. The mesh belt 72 is moved by rotation of the stretching rollers 74. While the mesh belt 72 continuously moves, the passing-through material having passed through the deposition unit 60 continuously accumulates, so that a web W is formed on the mesh belt 72. For example, the mesh belt 72 is formed of metal, resin, cloth, or nonwoven fabric.

The suction mechanism 76 is provided below the mesh belt 72 (on a side opposite from the deposition unit 60). The suction mechanism 76 can generate a downward airflow (an airflow flowing from the deposition unit 60 toward the mesh belt 72). By the suction mechanism 76, the mixture dispersed in the air by the deposition unit 60 can be sucked onto the mesh belt 72. This can increase the discharge speed from the deposition unit 60. Further, a downflow can be generated in a dropping path of the mixture by the suction mechanism 76, and this can prevent the defibrated material and the additive agent from tangling during dropping.

As described above, a soft and puffed web W containing much air is formed via the deposition unit 60 and the web forming unit 70 (web forming process). The web W deposited on the mesh belt 72 is transferred to the sheet forming unit 80.

In the example of FIG. 1, a moisture-adjusting unit 78 is provided to adjust the moisture in the web W. The moisture-adjusting unit 78 can adjust the amount ratio of the web W and water by adding water or vapor to the web W.

The sheet forming unit 80 forms a sheet S by pressurizing and heating the web W deposited on the mesh belt 72. In the sheet forming unit 80, the mixture of the defibrated material and the additive agent mixed in the web W is heated, so that a plurality of fibers in the mixture can be bonded with the additive agent (resin) being disposed therebetween.

As the sheet forming unit 80, for example, a heating roller (heater roller), a heat press forming apparatus, a hot plate, a warm air blower, an infrared heater, or a flash fixing device is used. In the example of FIG. 1, the sheet forming unit 80 includes a first bonding unit 82 and a second bonding unit 84, and each of the bonding units 82 and 84 has a pair of heating rollers 86. Since the bonding units 82 and 84 are formed by the heating rollers 86, a sheet S can be formed while continuously transferring the web W, in contrast to a case in which the bonding units 82 and 84 are formed by plate-like pressing devices (planar pressing devices). The number of heating rollers 86 is not particularly limited.

The cutting unit 90 cuts the sheet S formed by the sheet forming unit 80. In the example of FIG. 1, the cutting unit 90 includes a first cutting unit 92 for cutting the sheet S in a direction intersecting the transfer direction of the sheet S, and a second cutting unit 94 for cutting the sheet S in a direction parallel to the transfer direction. For example, the second cutting unit 94 cuts a sheet S that has passed through the first cutting unit 92.

Through the above procedure, a single sheet S of a predetermined size is formed. After cutting, the single sheet S is discharged to a discharge unit 96.

1.2. Detection Unit

A detection unit 91 in the sheet manufacturing apparatus 100 will be described in detail with reference to

FIGS. 2 and 3. FIG. 2 is a side view schematically illustrating a detection unit 91 and a switch unit 95 serving as a part of a forming unit 106 in the sheet manufacturing apparatus 100 according to the embodiment. FIG. 3 is a schematic plan view of the detection unit 91. In FIGS. 2 and 3, the deposition unit 60 and the sheet forming unit 80 located on the upstream side of the forming unit 106 in a transfer direction M are omitted, and the second cutting unit 94 located on the downstream side in the transfer direction M is omitted. In the following description, the terms “upstream side” and “downstream side” refer to “upstream side in the transfer direction M” and “downstream side in the transfer direction M”, respectively.

The forming unit 106 of the sheet manufacturing apparatus 100 illustrated in FIG. 2 includes the deposition unit 60, the web forming unit 70, the sheet forming unit 80, the cutting unit 90, and the discharge unit 96 that have been described with reference to FIG. 1. In FIG. 2, the cutting unit 90 and the discharge unit 96 are illustrated. The forming unit 106 forms a continuous sheet S1 (a single sheet S2) by depositing, pressurizing, and heating a material containing fibers. As illustrated in FIG. 2, the forming unit 106 further includes a detection unit 91 and a switch unit 95 provided between the sheet forming unit 80 and the discharge unit 96 illustrated in FIG. 1.

The detection unit 91 detects the texture of a continuous sheet S1. By detecting the texture of the continuous sheet S1 in the detection unit 91, for example, a defective sheet that does not meet a predetermined standard can be detected. When the detection unit 91 is disposed on the downstream side of the first cutting unit 92, it detects the texture of a single sheet S2.

Here, the term “texture (uniformity)” refers to the quality (formation) of the continuous sheet S1 or the single sheet S2. Specifically, the term “texture” refers to the degree (extent) of a difference in shade that is seen when light is applied from one surface of the continuous sheet S1, as shown in an experimental example to be described later. That is, “a sheet having a relatively good texture” refers to a continuous sheet S1 or a single sheet S2 with which this difference in shade is small.

The detection unit 91 is an optical sensor that emits light from one surface side of the continuous sheet S1 and receives the light on the other surface side. In the detection unit 91 of FIG. 2, a light source unit 91 a is disposed above the continuous sheet S1, and a reading unit 91 b is disposed at a position opposed to the light source unit 91 a with the continuous sheet S1 being disposed therebetween. The reading unit 91 b receives light having passed through the continuous sheet S1, of the light emitted from the light source unit 91 a.

The light source unit 91 a is a known light source used in an optical sensor. As the light source unit 91 a, for example, a light emitting diode (LED) or a semiconductor laser diode (LD) can be used.

The reading unit 91 b can change the output according to the intensity of received light (light having passed through the continuous sheet S1), and can be formed by a known photodetector used in the optical sensor. For example, such a photodetector can be formed by a CCD line sensor capable of using the photoelectric effect and composed of light receiving elements arranged in line or an area sensor capable of performing two-dimensional detection and composed of light receiving elements arranged in vertical and horizontal directions.

The reading unit 91 b can detect the texture over the entire surface of the continuous sheet S1. That is, after the continuous sheet S1 is cut in the first cutting unit 92, the reading unit 91 b detects the texture of the entire surface of a single sheet S2. By detecting the entire surface of the continuous sheet S1 with the reading unit 91 b, even when a part of the continuous sheet 81 has a defect, the defect can be detected.

Here, the term “entire surface” of the continuous sheet S1 may literally refer to the entire surface, or may refer to the substantially entire surface. For example, the substantially entire surface of the continuous sheet S1 may be a part of the continuous sheet S1 to become a product (that is, the entire surface of the single sheet S2).

As illustrated in FIG. 3, the detection unit 91 is disposed all over the full width of the continuous sheet S1, or is disposed to detect the texture at least over a full width SW of the single sheet S2. When the reading unit 91 b is a line sensor, the texture of the entire surface of the continuous sheet S1 can be detected by performing reading at a predetermined cycle in accordance with the moving speed of the continuous sheet S1 in the transfer direction M.

The reading unit 91 b outputs information about the detected light to the control unit 140. The control unit 140 can control the downstream operation units on the basis of the information from the reading unit 91 b.

Since the detection unit 91 is disposed on the upstream side of the first cutting unit 92, the continuous sheet S1 is an object in the detection unit 91. However, the position of the detection unit 91 is not limited thereto. For example, when the detection unit 91 is disposed on the downstream side of the second cutting unit 94, the object may be a cut single sheet S2.

1.3. First Cutting Unit

The first cutting unit 92 includes a blade unit 92 b having, at its lower end, a blade for cutting the continuous sheet S1, and a cutting drive unit 92 a for moving the blade unit 92 b up and down relative to the continuous sheet S1. The blade unit 92 b has a blade extending over the full width of the continuous sheet S1 in the direction intersecting the transfer direction M. While the first cutting unit 92 will be described as a so-called guillotine cutter as an example, a known paper cutting mechanism, such as a rotary cutter using a rotating disc-like blade, can be adopted.

The first cutting unit 92 is disposed on the downstream side of the detection unit 91. The first cutting unit 92 is disposed between rollers 93 a that continuously rotate to send out a continuous sheet S1 and rollers 93 b that continuously or intermittently rotate to send out a single sheet S2. On the downstream side of the first cutting unit 92, the unillustrated second cutting unit 94 is disposed to perform cutting along the transfer direction M of the continuous sheet S1. The second cutting unit 94 cuts both widthwise ends of the single sheet S2, and is different from the first cutting unit 92 only in the cutting direction. Hence, the second cutting unit 94 can adopt a mechanism similar to that of the first cutting unit 92.

1.4. Switch Unit

As illustrated in FIG. 2, the switch unit 95 is provided between the detection unit 91 and the discharge unit 96 and on the downstream side of the cutting unit 90. For example, the switch unit 95 is disposed at a position on the downstream side of the rollers 93 b that push out single sheets S2 cut by the first cutting unit 92 in the direction orthogonal to the transfer direction M.

The switch unit 95 includes a guide plate 95 a for guiding lower surfaces of the cut single sheets S2. In FIG. 2, the guide plate 95 a in a state shown by a solid line forms at least a part of a first path 95 b serving as a transfer path for the single sheets S2, and the guide plate 95 a in a state shown by a broken line forms at least a part of a second path 97 a serving as a transfer path for the single sheets S2.

The first path 95 b guides the single sheets S2 to the discharge unit 96 via the rollers 93 c. The discharge unit 96 includes a stack unit 96 a on which the single sheets S2 are to be stacked.

The second path 97 a guides the single sheets S2 to a collecting unit 97. The collecting unit 97 may be a box that can accommodate the single sheets S2.

The switch unit 95 can distribute the single sheets S2 to the first path 95 b or the second path 97 a by swinging the guide plate 95 a up and down according to a command from the control unit 140, as illustrated in FIG. 2. The control unit 140 gives the command to the switch unit 95 by determining, on the output from the reading unit 91 b of the detection unit 91, whether or not the texture of a single sheet S2 detected in the control unit 140 is good.

For example, when the texture of a single sheet S2 is relatively good, the control unit 140 sets the guide plate 95 a to the first path 95 b to guide the single sheet S2 to the stack unit 96 a. When the texture of the single sheet S2 is relatively bad, the control unit 140 turns the guide plate 95 a to the second path 97 a to guide the single sheet S2 to the second path 97 a so that the single sheet S2 does not reach the stack unit 96 a. Since the single sheet S2 having a relatively bad texture is guided to the path different from the path for the single sheet S2 having a relatively good texture, it can be separated from the single sheet S2 having the relatively good texture.

Although not illustrated, the control unit 140 includes an operating unit to be operated by the user, an output unit that displays, for example, processing results of the operation units, a storage unit that stores data on the texture as the criterion for quality judgment and programs for the units, a storage medium that stores various application programs and data and that can be read by a computer, and a processing unit that performs various control operations according to the programs stored in the storage unit and the storage medium. For example, the processing unit can be implemented as hardware, such as various processors (for example, a CPU and a DSP) and an ASIC (for example, a gate array), or as programs.

While the collecting unit 97 is provided in the second path 97 a, the structure is not limited thereto. A transfer path may be provided to return a single sheet S2 having a relatively bad texture to the crushing unit 12 illustrated in FIG. 1.

The switch unit 95 may be disposed on the upstream side of the second cutting unit 94 that is not illustrated in FIG. 2. This is because such cutting with the second cutting unit 94 is unnecessary for a defective single sheet S2 that does not become a product and the lifetime of the cutter of the second cutting unit 94 is increased by omitting cutting of the single sheet S2 judged defective.

1.5. Sheet Manufacturing Method

A sheet manufacturing method forms a continuous sheet S1 (a single sheet S2) by depositing, pressurizing, and heating a material containing fibers, and detects the texture of the continuous sheet S1 (single sheet S2).

The sheet manufacturing method can be carried out by the sheet manufacturing apparatus 100.

First, when the user requests an operation for manufacturing a sheet S through the use of the unillustrated operating unit in the control unit 140, the control unit 140 starts operations of the operation units.

The control unit 140 receives an output signal from the detection unit 91, and determines whether the texture of a continuous sheet S1 is relatively good or relatively bad. When the control unit 140 determines that the continuous sheet S1 is “a relatively good sheet”, it operates the guide plate 95 a of the switch unit 95 to discharge single sheets S2, which are obtained by cutting the continuous sheet S1, to the stack unit 96 a of the discharge unit 96 in the first path 95 b. Further, when the control unit 140 determines that the continuous sheet S1 is “a relatively bad sheet”, it operates the guide plate 95 a of the switch unit 95 to guide single sheets S2, which are obtained by cutting the continuous sheet S1, to the second path 97 a.

In this way, according to this sheet manufacturing method, the texture of the continuous sheet S1 (single sheet S2) can be detected, and a defective sheet can be detected by using the detection result.

As illustrated in FIG. 3, the detection unit 91 detects the texture in the width SW serving as the full width of the single sheet S2 (a width except for diagonally shaded areas in FIG. 3 to be cut and removed). Since the diagonally shaded areas are not production parts, they do not need to be used for quality judgment of the texture. Further, since deposition of the raw material in the defibrating unit 20 (see FIG. 1) is relatively likely to become uneven in the diagonally shaded areas, the diagonally shaded areas are preferably not used for quality judgment of the texture.

Next, a texture quality judging method will be described.

1.6. Quality Judging Method

FIG. 4A is a graph showing the intensity of transmitted light in the widthwise direction of the continuous sheet S1, which is detected by the reading unit 91 b of the detection unit 91. The horizontal axis shows the width SW of the continuous sheet S1, and the vertical axis shows the intensity of transmitted light detected by the reading unit 91 b.

Although the graph of FIG. 4A can be used for quality judgment of the texture as it is, since it sometimes includes noise, noise is preferably removed to some extent by applying a known noise removing method.

The graph of FIG. 4B is obtained by subjecting the graph of FIG. 4A to moving-averaging processing. The horizontal axis and the vertical axis are the same as those of FIG. 4A. In the graph of FIG. 4B, more noise is removed than in the graph of FIG. 4A.

The control unit 140 prestores data serving as the criterion for quality judgment of the texture. In FIG. 4B, the upper limit and the lower limit are set at a predetermined reference ratio to the average value of measured intensities of transmitted light, and are shown by broken lines. When transmitted light out of the range between the upper limit and the lower limit is detected, the control unit 140 determines that a defect DF exists in a portion corresponding to the transmitted light, and determines that a single sheet S2 including the defect DF is “a relatively bad sheet.”

For example, such a defect DF appears as a block dot on the single sheet S2 illustrated in FIG. 3.

By measuring such linear data in accordance with the moving speed of the continuous sheet S1, the texture of the entire surface of the continuous sheet S1 can be measured and judged without any gap.

Alternatively, when the control unit 140 calculates a standard deviation of the sheet by using the data of FIG. 4B and the standard deviation is larger than a standard deviation serving as an acceptabililty criterion for determining that the sheet is “a relatively good sheet”, which is prestored in the control unit 140, it may be determined that the sheet is “a relatively bad sheet.”

While the control unit 140 makes determination on the basis of the linear data in the direction orthogonal to the transfer direction M of the continuous sheet S1 herein, determination may be made on the basis of data on a sheet plane of a predetermined length in the transfer direction M of the continuous sheet S1 (for example, the length of a single sheet S2) instead. For example, a histogram of the intensity of transmitted light in the sheet plane of the single sheet S2 can be obtained by adding the data of FIG. 4A, as illustrated in FIG. 5. In FIG. 5, the horizontal axis shows the intensity of transmitted light, and the vertical axis shows the frequency.

FIG. 5 shows that the standard deviation shown by a solid line more greatly varies than the standard deviation shown by a broken line and the transmitted light in the sheet plane is uneven. It can be considered that unevenness of the transmitted light corresponds to the variation in thickness of the single sheet S2 and to the variation in deposition of the raw material.

Here, an acceptabililty reference standard deviation for “a relatively bad sheet” is obtained beforehand by actual measurement, and is stored in the control unit 140. The standard deviation obtained as shown in FIG. 5 is compared with the reference standard deviation. When the standard deviation is larger than the reference standard deviation, it is determined that the sheet is “a relatively bad sheet.” For example, the standard deviation σ is 6.9 in the graph shown by the broken line in FIG. 5, and the standard deviation σ is 9.3 in the graph shown by the solid line. When the reference standard deviation σ serving as the acceptabililty criterion is set at 7.0 or less, a single sheet S2 shown by the graph of the broken line is judged as “a relatively good sheet”, and a single sheet S2 shown by the graph of the solid line is judged as “a relatively bad sheet.”

2. First Modification of Sheet Manufacturing Apparatus

FIG. 6 is a side view schematically illustrating a detection unit 91 and an application unit 98 in a first modification of the sheet manufacturing apparatus 100 of the embodiment. In FIG. 6, a deposition unit 60, a sheet forming unit 80, and so on located on the upstream side of the detection unit 91 are not illustrated.

The sheet manufacturing apparatus 100 includes an application unit 98 for applying a marking on a continuous sheet S1 having a relatively bad texture. The application unit 98 is disposed on the downstream side of the detection unit 91 and rollers 93 a provided downstream of the detection unit 91 to convey the continuous sheet S1. On the downstream side of the application unit 98, a take-up unit 96 b is provided to take up the continuous sheet S1 around a take-up roller 96 c.

When the control unit 140 determines that the continuous sheet S1 is “a sheet having a relatively bad texture”, according to a command from the control unit 140, for example, the application unit 98 applies a marking near a position on the continuous sheet S1 where a defect is judged as being present, or applies a marking on a predetermined position on “a relatively bad sheet” including the defect when the continuous sheet S1 is cut into a single sheet S2. By such marking with the application unit 98, it can be recognized that the texture is bad.

A known method can be used for marking in the application unit 98, and a marking may be not only a character for representing a defective product but also a sign or a symbol, such as a bar code, as long as the marking is to be printed. Instead of a printed marking, embossing or hole machining may be used.

Instead of the take-up unit 96 b, a cutting unit 90, a switch unit 95, a discharge unit 96, and a collecting unit 97 illustrated in FIGS. 1 and 2 may be adopted. In this case, single sheets S2 collected in the collecting unit 97 are sheets marked as “a relatively bad sheet.”

While the dry method is used in the above-described embodiment, the sheet manufacturing apparatus of the invention may adopt a wet method. For example, a disaggregating unit (pulper) may be used instead of the defibrating unit 20, a deinking unit may be used as the classifying unit 30, and a papermaking unit may be used as the sheet forming unit 80.

Sheets S1, S1, and S2 manufactured by the sheet manufacturing apparatus of the invention mainly refer to sheet-like materials. However, the sheets are not limited to sheet-like materials, and may be board-like or web-like materials. In this specification, sheets are classified into paper and nonwoven fabric. Paper includes a thin sheet formed using pulp or waste paper as a raw material, and examples of paper include recording paper for writing and printing, wall paper, wrapping paper, colored paper, drawing paper, and Kent paper. Nonwoven fabric has a larger thickness and a lower strength than paper, and examples of nonwoven fabric include popular nonwoven fabric, a fiber board, tissue paper (cleaning tissue paper), kitchen paper, a cleaner, a filter, a liquid (waste ink and oil) absorbing material, a sound absorbing material, a thermal insulating material, a cushioning material, and a mat. The raw material may be plant fiber, such as cellulose, chemical fiber, such as PET (polyethylene terephthalate) or polyester, and animal fiber such as wool or silk.

In the invention, it is possible to partly omit the configuration and to combine the embodiments and the modifications within the scope including the features and advantages described in the application.

The invention includes substantially the same configuration as the configuration described in the embodiment (for example, a configuration having the same functions, methods, and results, or a configuration having the same object and effects). The invention includes a configuration obtained by replacing the non-essential parts of the configuration described in the embodiment. The invention includes a configuration for realizing the same operation results or a configuration for obtaining the same object as that of the configuration described in the embodiment. The invention includes a configuration obtained by adding the known art to the configuration described in the embodiment.

The entire disclosure of Japanese Patent Application No. 2014-252769, filed Dec. 15, 2014 is expressly incorporated by reference herein. 

What is claimed is:
 1. A sheet manufacturing apparatus comprising: a forming unit configured to form a sheet by depositing, pressurizing, and heating a material containing fiber; and a detection unit configured to detect a texture of the sheet.
 2. The sheet manufacturing apparatus according to claim 1, wherein the detection unit is an optical sensor configured to emit light from a side of one surface of the sheet, receive the light on a side of the other surface of the sheet, and detect the texture of an entire surface of the sheet.
 3. The sheet manufacturing apparatus according to claim 1, further comprising: a stack unit on which the sheet is stacked when the texture of the sheet is relatively good; and a path configured to prevent the sheet from going to the stack unit when the texture of the sheet is relatively bad.
 4. The sheet manufacturing apparatus according to claim 1, further comprising: an application unit configured to apply a marking on the sheet when the texture of the sheet is relatively bad.
 5. A sheet manufacturing method comprising: forming a sheet by depositing, pressurizing, and heating a material containing fiber; and detecting a texture of the sheet. 